COVENEY, RAYMOND M., JR.
University of Missouri, Kansas City MO
Abstract: Genetic Connections between Ores, Hydrocarbon Deposits, Black Shales and Migrating Basinal Brines
Paleozoic strata of the Midwest host (1) Mississippi Valley-type (MVT) ore deposits and fossil fuel resources which are localized in discrete mining districts and hydrocarbon fields, (2) widespread country-rock occurrences of ~60-150 degrees C fluid inclusions containing brines and hydrocarbons, and (3) extremely metal-rich black shales which occur in Mississippian strata but which are especially prevalent in overlying Pennsylvanian cyclothems throughout the Midwest.
In the past, the lack of key petrographic information and the paucity of absolute dates for some of the most important deposits, the MVT ores, has hampered the development of a coherent hypothesis relating these phenomena. The discovery of additional occurrences of hydrothermal minerals and the availability of key radiometric dates has led to the development of a genetic model which begins with the early introduction of certain metal values, such as Zn and Ba, from migrating basinal brines to shales and surrounding rocks during sedimentation and early diagenesis. Substantial augmentation of metal values in permeable beds, including thin jointed black shales, likely took place at a later time. Consequent plugging of numerous minor passageways in carbonate and shale beds may have been a major factor in confining the subsequent development of major ore and hydrocarbon deposits within discrete locations.
AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas